My take (just from the provided page and not from further context) is that Gates was saying MS does not do a new version of software on the basis of / for the sole or primary purpose of fixing bugs. This does not mean they do not fix bugs in a new version. It means fixing bugs is NOT the motivation for doing a new version. Bug fixes do not provide sufficient motivation for users to purchase the new version.

EDIT: I did not mean for my comment to be a child to this parent. Clicked wrong when beginning it.